Process for manufacturing inorganic article, inorganic article, and circuit substrate

ABSTRACT

A process for manufacturing an inorganic material-based article comprising the steps of  
     (1) forming a sol solution mainly composed of an inorganic component,  
     (2) producing inorganic material-based gel fine fibers by extruding the resulting sol solution from a nozzle, and at the same time, applying an electrical field to the extruded sol solution to thin the extruded sol solution, and then, collecting inorganic material-based gel fine fibers on a support,  
     (3) drying the collected inorganic material-based gel fine fibers to produce inorganic material-based article containing inorganic material-based dried gel fine fibers, and then,  
     (4) sintering the inorganic material-based article containing inorganic material-based dried gel fine fibers to produce inorganic material-based article containing inorganic material-based sintered fine fibers.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process for manufacturing aninorganic material-based article consisting of or composed mainly ofinorganic material-based fine fibers, and an inorganic material-basedarticle which may be prepared by the above-mentioned process andconsists of or is composed mainly of inorganic material-based ultra-finelong fibers.

[0003] 2. Description of the Related Art

[0004] For example, an inorganic material-based sheet composed ofinorganic material-based short fibers, such as glass short fibers, isfavorably used as a filter or a separator in a lead accumulator, becauseof excellent filtering and separating properties.

[0005] The inorganic material-based short-fibers sheet was prepared, forexample, by forming a sheet from material-based short-fibers inaccordance with a wed-laid method. There is a possibility that someinorganic material-based short-fibers are dropped from the inorganicmaterial-based short-fibers sheet prepared by the above-mentionedprocess. Therefore, it is preferable to bond inorganic material-basedshort-fibers by an adhesive. When the adhesive is used, however, therewere disadvantages in that the adhesive is eluted, or applications ofthe inorganic material-based short-fibers sheet was limited.

[0006] For example, Sumio Sakka, “Zoru-Geru Hou no Kagaku (Science of asol-gel method)” published by Agune-Shofu, Jul. 5, 1988, discloses thatshort fibers having a diameter of 10 μm and a length of at most 20 mmcan be prepared (pages 78-79). Nevertheless, there is a possibility thatsome short fibers are dropped from a fiber sheet prepared from suchshort fibers, because of shortness, and if an adhesive is used, therewere disadvantages in that the adhesive is eluted, or applications ofthe inorganic material-based short-fibers sheet was limited.

[0007] For example, when the inorganic material-based short-fibers sheetis used as a filter in a clean room, eluted substances may be adhered toa surface of a silicon wafer or a glass substrate. In some cases, theinorganic material-based short-fibers sheet cannot be used as aheat-resistant filter, because an adhesive is not heat-resistant.

[0008] Furthermore, the inorganic material-based short-fibers in priorart have a large diameter, and do not have pliability. Therefore, ashape of the article of the inorganic material-based short-fibers islimited to a sheet or a plate, and the application is also limited.

[0009] Recently, miniaturization and high performance of a semiconductoror an electronic component such as a circuit board mounted on a computeris desired due to the miniaturization and high performance of industrialor personal electronic equipment. For the miniaturization of theelectronic component, it is important to thin the circuit board and tomake wiring denser. Therefore, the material for the circuit board isrequired to have a reliable insulation quality enabling a thinning ofline pitches, and a laser workability enabling the miniaturization ofholes.

[0010] Hitherto, a glass-epoxy circuit board prepared by impregnating asubstrate of a glass fibers woven fabric or a glass fibers nonwovenfabric with an epoxy resin was widely used as a circuit board carryingelectronic components. Nevertheless, the glass-epoxy circuit board hasdisadvantages that, when holes are produced by a laser, a shape of theproduced hole may not be accurate, or a fuzzing may occur.

[0011] Recently, a circuit board of organic fibers such as an aramidfiber attracted attention because of an excellent resistance to thermalexpansion and a laser workability. Nevertheless, an aramide fiber has ahigh hygroscopity, and disadvantageously, the circuit board lacksreliable insulation quality.

SUMMARY OF THE INVENTION

[0012] Accordingly, the object of the present invention is to remedy thedisadvantages in prior art and provide a process for manufacturing-aninorganic material-based article which can avoid an adhesive and remedythe disadvantages caused by the adhesive used in prior art.

[0013] Another object of the present invention is to provide aninorganic material-based article having an excellent pliability fromwhich fibers are hardly dropped, or pollutants derived from an adhesiveare hardly released.

[0014] Still another object of the present invention is to provide acircuit board having an excellent reliable insulation quality and alaser workability, and sufficiently meeting the recent requirement forthe miniaturization and high performance.

[0015] Still another object of the present invention is to provide asubstrate for the circuit board.

[0016] Other objects and advantages of the present invention will beapparent from the following description.

[0017] In accordance with the present invention, there is provided aprocess for manufacturing an inorganic material-based article comprisingthe steps of

[0018] (1) forming a sol solution mainly composed of an inorganiccomponent [hereinafter sometimes referred to a sol solution formingstep],

[0019] (2) producing inorganic material-based gel fine fibers byextruding the resulting sol solution from a nozzle, and at the sametime, applying an electrical field to the extruded sol solution to thinthe extruded sol solution, and then, collecting inorganic material-basedgel fine fibers on a support [hereinafter sometimes referred to acollecting step], and then,

[0020] (3) drying the collected inorganic material-based gel fine fibersto produce inorganic material-based article containing inorganicmaterial-based dried gel fine fibers [hereinafter sometimes referred toa drying step], and/or

[0021] (4) sintering the collected inorganic material-based gel finefibers or the inorganic material-based article containing inorganicmaterial-based dried gel fine fibers to produce inorganic material-basedarticle containing inorganic material-based sintered fine fibers[hereinafter sometimes referred to a sintering step].

[0022] According to the manufacturing process of the present invention,the inorganic material-based article can be prepared by the dryingand/or sintering without an adhesive, and therefore, the disadvantagescaused by the adhesive can be avoided.

[0023] According to a preferable embodiment of the manufacturing processof the present invention, the support used in the collecting step (2)has a three-dimensional structure. The resulting inorganicmaterial-based article has a three-dimensional structure, and can beapplied to various fields.

[0024] In accordance with the present invention, there is also providedan inorganic material-based article comprising inorganic material-basedultra-fine long fibers having an average fiber diameter of 2 μm or less,and composed mainly of an inorganic component.

[0025] As above, the inorganic material-based article according to thepresent invention comprises long fibers, and thus the fibers are hardlydropped therefrom. Further, a diameter of the fiber is as small as 2 μmor less, and the article has an excellent pliability, may have variousshapes, and can be applied to various fields.

[0026] According to a preferable embodiment of the inorganicmaterial-based article, contacting surfaces of the inorganicmaterial-based ultra-fine long fibers are bonded to each other not viaan adhesive, i.e., without an adhesive. In a preferable embodiment, theinorganic material-based article does not substantially contain anadhesive. Therefore, the article will hardly release pollutants.

[0027] According to another preferable embodiment of the inorganicmaterial-based article, a CV value of the inorganic material-basedultra-fine long fiber in the inorganic material-based article is 0.8 orless. The inorganic material-based article composed of the inorganicmaterial-based ultra-fine long fibers having a CV value of 0.8 or lesshas uniform properties.

[0028] In accordance with the present invention, there is also provideda substrate for a circuit board, comprising a fiber sheet containinginorganic material-based ultra-fine fibers having an average fiberdiameter of 2 μm or less, and composed mainly of an inorganic component.

[0029] A glass fiber in a glass woven fabric or a glass nonwoven fabricused in a conventional substrate for a circuit board has a thickdiameter, in view of stability upon spinning or workability. The lowerlimitation is as large as about 5 μm. Therefore, when a laser processingis carried out, the shape of the hole cannot be accurately controlled,or fuzzing may occur. On the contrary, the present substrate for acircuit board is formed from the inorganic material-based ultra-finefibers having an average fiber diameter of 2 μm or less, and thus alaser processing can be carried out without encountering the problems ofthe control of the shape of the hole or fuzzing. The present substrateprovides workability as a substrate made of organic fibers in a laserprocessing. Further, the inorganic material-based ultra-fine fibers arecomposed mainly of the inorganic component, and the present substratefor a circuit board has a highly reliable insulation quality.

[0030] According to a preferable embodiment of the present substrate fora circuit board, a silica component contained in the material-basedultra-fine fiber is 50 mass % or more. Therefore, various glasscompositions from, for example, a conventional E glass composition to aconventional Q glass (silica glass) composition may be selecteddependently of various applications of the circuit board. Particularly,when the silica glass composition is used, a circuit board having adielectric constant suitable for a high-frequency and a low dielectricdissipation factor can be manufactured.

[0031] According to another preferable embodiment of the presentsubstrate for a circuit board, the fiber sheet has a structure of anonwoven fabric. A structure of a glass woven fabric inevitably includescrossing portions of glass yarns. The crossing portions affectsmoothness. Further, an apparent density is high, and a matrix resin isdifficult to penetrate. On the contrary, the present substrate for acircuit board has the structure of a nonwoven fabric, and thus has anexcellent smoothness and an excellent permeability of a resin.

[0032] According to still another preferable embodiment of the presentsubstrate for a circuit board, the fiber sheet consists essentially ofthe inorganic material-based ultra-fine fibers, that is, does notsubstantially contain any component other than the inorganicmaterial-based ultra-fine fibers. A conventional glass nonwoven fabriccontains an adhesive, and a formation of a coating of the resin causes apoor penetration of a matrix resin into a substrate for a circuit board.On the contrary, the present substrate for a circuit board can provide agood penetration, and does not elute pollutants from an adhesive.Therefore, a circuit board having an excellent insulating property canbe manufactured.

[0033] According to still another preferable embodiment of the presentsubstrate for a circuit board, the inorganic material-based ultra-finefibers consist essentially of long fibers. Therefore, the fuzzing may bereduced in a step of impregnating with a matrix resin or a step ofprocessing a circuit board.

[0034] According to still another preferable embodiment of the presentsubstrate for a circuit board, a thickness of the substrate is 80 μm orless. Therefore, a thickness of a circuit board can be lowered, and theminiaturization of a space for a circuit board can be realized.

[0035] In accordance with the present invention, there is also provideda circuit board containing the above-mentioned substrate. The presentcircuit board has excellent properties as mentioned above.

BRIEF DESCRIPTION OF DRAWINGS

[0036]FIG. 1 schematically illustrates an embodiment of the process formanufacturing an inorganic material-based article of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] In the manufacturing process according to the present invention,the sol solution forming step (1) is carried out at first. That is, thesol solution composed mainly of an inorganic component is formed. Theexpression “composed mainly of an inorganic component” as used hereinmeans that the inorganic component is contained at an amount of 50 mass% or more. An amount of the inorganic component in the sol solution ispreferably 60 mass % or more, more preferably 75 mass % or more.

[0038] The sol solution may be prepared by hydrolysis, at about 100° C.or less, of a solution (stock solution) of a compound containing one ormore elements to be included in the inorganic material-based dried gelfine fibers or the inorganic material-based sintered fine fibers formingthe inorganic material-based article finally manufactured by the processaccording to the present invention, and then condensationpolymerization. A solvent of the solution may be an organic solvent suchas alcohol, or water.

[0039] The element contained in the compound is not particularlylimited, but for example, lithium, beryllium, boron, carbon, sodium,magnesium, aluminum, silicon, phosphorus, sulfur, potassium, calcium,scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel,copper, zinc, gallium, germanium, arsenic, selenium, rubidium,strontium, yttrium, zirconium, niobium, molybdenum, cadmium, indium,tin, antimony, tellurium, cesium, barium, lanthanum, hafnium, tantalum,tungsten, mercury, thallium, lead, bismuth, cerium, praseodymium,neodymium, promethium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium or lutetium.

[0040] The compound containing one or more the above-mentioned elementsmay be an oxide of the element, for example, SiO₂, Al₂O₃, B₂O₃, TiO₂,ZrO₂, CeO₂, FeO, Fe₃O₄, Fe₂O₃, VO₂, V₂O₅, SnO₂, CdO, LiO₂, WO₃, Nb₂O₅,Ta₂O₅, In₂O₃, GeO₂, PbTi₄O₃, LiNbO₃, BaTiO₃, PbZrO₃, KTaO₃, Li₂B₄O₇,NiFe₂O₄, SrTiO₃. The inorganic component may be composed of one or moreoxides as above, for example, two components such as SiO₂-Al₂O₃.

[0041] The sol solution may be obtained from the stock solution bycondensation polymerization of the above-mentioned compounds, and iscomposed mainly of an inorganic material. That is, the inorganiccomponents account for 50 mass % or more, preferably 60 mass % or more,more preferably 75 mass % or more. The sol solution must have aviscosity so that the sol solution can be spun from a nozzle in thecollecting step (2) as mentioned below. The viscosity is notparticularly limited, so long as the sol solution can be spun, butpreferably 0.1 to 100 poise, more preferably 0.5 to 20 poise,particularly preferable 1 to 10 poise, most preferably 1 to 5 poise. Ifthe viscosity is more than 100 poise, it becomes difficult to obtainfine fibers. If the viscosity is less than 0.1 poise, a fiber shapecannot be obtained. When a gas of a solvent same as or similar to thatof the stock solution is provided around a tip of a nozzle, the solsolution having a viscosity of more than 100 poise may be used.

[0042] In addition to the inorganic components, the sol solution used inthe process of the present invention may contain organic components, forexample, a silane coupling agent, an organic low-molecular compound suchas a dyestuff, an organic high-molecular compound such as polymethylmethacrylate. More particularly, when the compound contained in thestock solution is a silane compound, the sol solution may contain aproduct obtained by condensation polymerization of a silane compoundmodified with methyl or epoxy groups.

[0043] The stock solution may contain a solvent, for example, an organicsolvent such as alcohol such as ethanol, or dimethylformamide (DMF), orwater, for stabilizing the compound in the stock solution; water forhydrolyzing the compound in the stock solution; a catalyst, such ashydrochloric acid or nitric acid, for smoothly carry out hydrolysis; achelating agent for stabilizing the compound such as a metallic compoundin the stock solution; a silane coupling agent for stabilizing acompound; a compound for imparting various properties such as apiezoelectricity; an organic compound, such as polymethyl methacrylate,for improving adherence or pliability, or adjusting rigidity; or anadditive such as a dyestuff. The above-mentioned additives may be addedto the stock solution before, during or after the hydrolysis.

[0044] When tetraethoxy silane is used, spinning becomes difficult froma sol solution containing water at an amount (molar ratio) more fourtimes that of alkoxide. Therefore, water is contained at an amount notmore than four times that of alkoxide. Further, when a base is used as acatalyst, it becomes difficult to obtain a sol solution which may bespun. Therefore, it is preferable to use a catalyst other than a base. Areaction temperature of the sol solution forming step (1) is notparticularly limited, so long as it is less than a boiling point of thesolvent. When a reaction temperature is low, a reaction rate isappropriately lowered, and it becomes easier to prepare a sol solutionwhich can be easily spun. Nevertheless, if the reaction temperature istoo low, the reaction becomes difficult to proceed. The reactiontemperature is preferably 10° C. or more.

[0045] In the manufacturing process according to the present invention,the collecting step (2) is then carried out. That is, inorganicmaterial-based gel fine fibers are produced by extruding the resultingsol solution from a nozzle, and at the same time, applying an electricalfield to the extruded sol solution to thin the extruded sol solution,and then, inorganic material-based gel fine fibers are collected on asupport.

[0046] A diameter of the nozzle to extrude the sol solution may varywith the fiber diameter of the desired inorganic material-based driedgel fine fibers or the desired inorganic material-based sintered finefibers. For example, the fiber diameter of the inorganic material-baseddried gel fine fibers or the inorganic material-based sintered finefibers is 2 μm or less, the diameter of the nozzle is preferably 0.1 to3 mm.

[0047] The nozzle may be of metallic or non-metallic. When the metallicnozzle is used, the nozzle may be used as one of electrodes. When thenon-metallic nozzle is used, an electrode is placed in the nozzle toapply an electric field to the extruded sol solution.

[0048] After extruding the sol solution from the nozzle, an electricfield is applied to the extruded sol solution to thereby stretch andthin the solution, and produce the inorganic material-based gel finefibers. The electric field may vary with a fiber diameter of the desiredinorganic material-based dried gel fine fibers or the desired inorganicmaterial-based sintered fine fibers, a distance between the nozzle and asupport, a solvent of the stock solution, a viscosity of the solsolution, or the like, and thus is not particularly limited. Forexample, however, when the fiber diameter of the inorganicmaterial-based dried gel fine fibers or the inorganic material-basedsintered fine fibers is about 3 μm or less, the electric field ispreferably 0.5 to 5 kV/cm. When the electric field applied is larger,the inorganic material-based gel fine fibers having thinner fiberdiameter can be obtained in accordance with the increase of the electricfield. Nevertheless, if the electric field applied is more than 5 kV/cm,a dielectric breakdown may easily occur. If the electric field appliedis less than 0.5 kV/cm, a fiber shape may not be formed.

[0049] It is assumed that when the electric field is applied, anelectrostatic charges are accumulated in the sol solution, and the solsolution is electrically drawn to an electrode placed on the side of thesupport whereby the sol solution is stretched and thinned to produceinorganic material-based gel fine fibers. In particular, because the solsolution is electrically drawn, a drawing speed of the sol solution isaccelerated by the electric field, as the sol solution is brought closeto the support, whereby the gel fiber having a thin diameter isproduced. Further, an evaporation of the solvent also accelerates thethinning, and elevates an electrostatic density. The elevated densityproduces an electric repulsion which causes division of the fibers,whereby the fibers are further thinned. The present invention is notlimited by no means to the above assumption.

[0050] The electric field may be applied between, for example, thenozzle (the metallic nozzle per se or the electrode located in thenon-metallic nozzle) and the support by producing a potential differencetherebetween. For example, the potential difference may be produced byapplying a voltage to the nozzle and grounding the support, or applyinga voltage to the support and grounding the nozzle.

[0051] The inorganic material-based gel fine fibers thinned by applyingthe electric field are collected on the support. The support may be amere carrier on which the fibers are mounted, or a component carrierwith which the inorganic material-based gel fine fibers are integrated.The mere support may be a porous roll or a non-porous roll. The supportwhich may be used as the mere carrier or the component carrier is, forexample, a woven fabric, a knitted fabric, a nonwoven fabric, a porousfilm sheet, or a non-porous sheet, such as a film. The component supportmay be made of fibers, such as organic fibers or inorganic fibers, orthread. The support may have any shape, such as a plane structure or athree-dimensional structure. The “three-dimensional structure” means astructure other than that of a plane sheet, and is for example, athree-dimensionally shaped article prepared by incurvating and/orbending a plane sheet. Such a three-dimensional support may be appliedto various fields. For example, a bellows-like support prepared bybending a plane sheet may be favorably used in a manufacture of afilter. A cylindrical support may be favorably used in a manufacture ofa liquid filter, or a bowl-like support may be favorably used in amanufacture of a mask.

[0052] The support is preferably made of a conductive material, such asa metal, having a volume resistance of 10⁹ Ω or less, when used as oneof the electrodes. When a conductive material as an opposite electrodeis located on the reverse side of the support with respect to the nozzleside, the support is not necessarily conductive. In the latter case, thesupport may be brought into contact with or separated from theconductive material.

[0053] Before the inorganic material-based gel fine fibers extruded fromthe nozzle and thinned by the applied electric field arrive at thesupport, organic fibers or yarns, inorganic fibers or yarns, or powdermaterial may be sprayed to the inorganic material-based gel fine fibersby an air gun or the like. In this case, a mixture of the inorganicmaterial-based gel fine fibers and the sprayed fibers and/or powdermaterial may be collected on the support. The fibers and/or powdermaterial may be sprayed from any direction to the inorganicmaterial-based gel fine fibers. For example, the direction of sprayingthe fibers and/or powder material may be perpendicular or oblique to thedirection of the inorganic material-based gel fine fibers forwarding thesupport from the nozzle.

[0054] The powder material may be, for example, an inorganic powdermaterial, such as titanium dioxide, manganese dioxide, copper oxide,silicon dioxide, activated carbon, or a metal such as platinum, or anorganic powder material, such as an ion-exchange resin, a colorant, apigment, or a medicament. An average particle size of the powdermaterial is not particularly limited, but is preferably 0.01 to 100 μm,more preferably 0.05 to 10 μm. A catalyst function, an abrasivefunction, an adsorption function, or an ion-exchange function can beimparted by adding the powder material.

[0055] The direction of extruding the sol solution from the nozzlegenerally conforms to that of collecting the inorganic material-basedthinned gel fine fibers on the support. The directions are notparticularly limited. For example, the inorganic material-based gel finefibers may be substantially vertically moved from an upper nozzle to alower support, or from a lower nozzle to an upper support. Further, theinorganic material-based gel fine fibers may be substantiallyhorizontally extruded and moved. It is preferable that the direction forextruding the sol solution does not conform to the gravitationallyeffective direction so as to prevent the gel from dropping. Inparticular, it is more preferable that the sol solution is extruded to adirection opposite to or perpendicular to the gravitationally effectivedirection.

[0056] As above, the inorganic material-based article having excellentproperties such as a strength or an easiness of shaping can be preparedby mixing the inorganic material-based gel fine fibers and the sprayedfibers and/or powder material, or integrating the inorganicmaterial-based gel fine fibers and the component carrier.

[0057] In the manufacturing process according to the present invention,the drying step (3) is then carried out after the collecting step (2).That is, the inorganic material-based gel fine fibers collected in theabove collecting step (2) are dried to produce the inorganicmaterial-based article containing inorganic material-based dried gelfine fibers.

[0058] In the manufacturing process according to the present invention,the drying step (3) is carried out after the collecting step (2), andthen the sintering step (4) is carried out. That is, the inorganicmaterial-based gel fine fibers collected in the above collecting step(2) are dried to produce the inorganic material-based article containinginorganic material-based dried gel fine fibers, and subsequently, theinorganic material-based article containing inorganic material-baseddried gel fine fibers is sintered to produce inorganic material-basedarticle containing inorganic material-based sintered fine fibers.

[0059] Alternatively, in the manufacturing process according to thepresent invention, the sintering step (4) is carried out after thecollecting step (2), without carrying out the drying step (3). That is,the inorganic material-based gel fine fibers collected in the abovecollecting step (2) are sintered to produce the inorganic material-basedarticle containing inorganic material-based sintered fine fibers.

[0060] Therefore, there are two kinds of the inorganic material-basedarticle obtained by the manufacturing process according to the presentinvention, that is, the article containing the inorganic material-baseddried gel fine fibers or the article containing the inorganicmaterial-based sintered fine fibers.

[0061] The drying step (3) will be described at first.

[0062] When the inorganic material-based gel fine fibers collected inthe collecting step (2) is dried to produce the inorganic material-basedarticle containing the inorganic material-based dried gel fine fibers, adrying temperature may vary with the inorganic component in theinorganic material-based gel fine fibers, and is not particularlylimited, but is preferably a temperature below a decompositiontemperature of the organic components, for example about 200° C. orless. The drying step (3) may be carried out by heating in an oven orthe like, freeze-drying or supercritical drying.

[0063] In the drying step (3), the inorganic material-based gel finefibers are dried so that the inorganic material-based article having astrength appropriate to its application can be obtained. The inorganicmaterial-based gel fine fibers are bonded to each other by entanglementor by adhesion caused by the evaporation of the solvents.

[0064] In the drying step (3), the inorganic material-based gel finefibers are dried under the integrated condition with the support toobtain the inorganic material-based article containing the inorganicmaterial-based dried gel fine fibers integrated with the support; or theinorganic material-based gel fine fibers are dried on the support, andthe inorganic material-based dried gel fine fibers are separated fromthe support to obtain the inorganic material-based article consistingessentially of the inorganic material-based dried gel fine fibers. Inboth cases, the constituent fibers are bonded to each other without anadhesive, and the fibers are hardly dropped from the article.

[0065] In the manufacturing process according to the present invention,the sintering step (4) may be carried out after the collecting step (2),without carrying out the drying step (3). A sintering temperature mayvary with the inorganic component in the inorganic material-based gelfine fibers, and is not particularly limited. For example, when theinorganic material-based article containing inorganic components andorganic components is sintered in a range from about 200° C. or more toa temperature below a decomposition temperature of the organiccomponents, the inorganic material-based article containing remainedorganic components can be obtained, and thus, the resulting inorganicmaterial-based article can exhibit functions of the remained organiccomponents, such as improved adherence, pliability, adjusted rigidity,an optical function by a dyestuff, or water repellency. In the inorganicmaterial-based article obtained by sintering as above, the fibers arebonded by sintering to each other, and hardly dropped from the article.Further, when the inorganic material-based article containing inorganicmaterial-based dried gel fine fibers is sintered over a decompositiontemperature of the organic components, the inorganic material-basedarticle consisting essentially of the inorganic components and havingexcellent strength and heat resistance can be obtained.

[0066] More particularly, when the inorganic material-based gel finefibers composed of silica components containing organic components issintered at about 200 to 400° C., the silica sintered article containingremained organic components can be obtained, and thus, the resultinginorganic material-based article can exhibit functions of the remainedorganic components, such as improved adherence, pliability, adjustedrigidity, an optical function by a dyestuff, or water repellency. Whenthe inorganic material-based gel fine fibers are sintered at 800° C. ormore, the silica sintered article consisting essentially of theinorganic components can be obtained. It is preferable that theinorganic material-based gel fine fibers are sintered by graduallyelevating temperature, because some inorganic material-based gel finefibers may be suddenly shrunk and damaged, when the inorganicmaterial-based gel fine fibers are sintered at a sintered temperaturewithout a gradual elevation of the temperature.

[0067] In the manufacturing process according to the present invention,it is possible to carry out the drying step (3) and then the sinteringstep (4) after the collecting step (2). In this case, the procedure toobtain the inorganic material-based article containing the inorganicmaterial-based dried gel fine fibers in the first drying step (3) may becarried out as the drying step (3) singly carried out as mentionedabove. Further, the procedure to obtain the inorganic material-basedarticle containing the inorganic material-based sintered fine fibers inthe second sintering step (4) may be carried out as the sintering step(4) singly carried out as mentioned above. In the second sintering step(4) carried out after the first drying step (3), the inorganicmaterial-based article containing the inorganic material-based dried gelfine fibers is treated. Therefore, it is not necessary to graduallyelevate the temperature. By successively carrying out the drying step(3) and the sintering step (4), the inorganic material-based articlecontaining the inorganic material-based sintered fine fibers having theremained organic components, or the inorganic material-based articleconsisting essentially of the inorganic components and having anexcellent strength and heat resistance can be obtained.

[0068] The inorganic material-based dried fine fibers or the inorganicmaterial-based sintered fine fibers obtained by the manufacturingprocess according to the present invention may contain inorganic ororganic fine particles therein. The fine particles may be producedduring forming the sol solution by hydrolysis, or mixed before extrudingthe sol solution from the nozzle.

[0069] The fine particle may be, for example, an inorganic fineparticle, such as titanium dioxide, manganese dioxide, copper oxide,silicon dioxide, activated carbon, or a metal such as platinum, or anorganic fine particle, such as a colorant, or a pigment. An averageparticle size of the fine particle is not particularly limited, but ispreferably 0.001 to 1 μm, more preferably 0.002 to 0.1 μm. An opticalfunction, porosity, a catalyst function, an adsorption function, or anion-exchange function can be imparted by adding the fine particles.

[0070] The manufacturing process according to the present invention willbe explained, referring to FIG. 1 which is a sectional viewschematically illustrating the manufacturing apparatus.

[0071] The sol solution prepared as mentioned above is supplied from thesol solution tank 1 to metallic nozzles 21 to 24 by a constant deliverypump or the like. An amount supplied to the nozzles 21 to 24 is notparticularly limited, but for example, may vary from 0.01 to 100 mL/hper a nozzle. Although the embodiment as shown in FIG. 1 has fournozzles, the number of nozzle is not particularly limited, that is, oneor more.

[0072] The sol solution supplied to the nozzles 21 to 24 is extrudedtherefrom. Further, a voltage is applied to the nozzles 21 to 24. Moreparticularly, the opposite electrode 3 located on the reverse side ofthe support 4 with respect to the side of the nozzles 21 to 24 isgrounded, an electric field is formed between the support 4 and themetallic nozzles 21 to 24 connected to the source 30. The extruded solsolution is stretched and thinned by the electric field to form theinorganic material-based gel fine fibers. A distance between the nozzles21 to 24 and the support 4 may be changed in a range preferably fromabout 10 mm to about 500 mm, more preferably from about 50 mm to about300 mm so as to adjust an electric strength from 0.5 to 5 kV/cm.Alternatively, it is possible to ground the nozzles 21 to 24 and apply avoltage to the opposite electrode 3.

[0073] When tips of the nozzles 21 to 24 are dried, the sol solution iseasily cured, and thus a stable spinning becomes difficult. Therefore,it is preferable that a gas of a solvent same as or similar to that ofthe stock solution is provided around the tips of nozzles, or ahigh-boiling point solvent, such as butanol, having a boiling point of100° C. or more is added to the sol solution, whereby the tips of thenozzles 21 to 24 are prevented from dried although not shown in FIG. 1.

[0074] The inorganic material-based gel fine fibers extruded from thenozzles 21 to 24 are collected on the support 4. The support 4 may be,for example a net endless belt, and moved in the direction of an arrow dby the roller 41, 42, 43 rotating to the directions of an arrow a, anarrow b and an allow c. An amount of the inorganic material-based gelfine fibers collected on the support may be adjusted by a moving speedof the net belt, an amount of the sol solution extruded from the nozzle,the number of the nozzles, or the like.

[0075] The inorganic material-based gel fine fibers collected on thesupport 4 are moved to a heating station, for example a heater 5, by themovement of the support 4, and dried by a heat of the heater 5 to obtainthe inorganic material-based article containing the inorganicmaterial-based dried gel fine fibers, i.e., a sheet containing theinorganic material-based dried gel fine fibers. It is preferable thatthe portion containing the heater 5 is separated as a heating room 8from the other portions.

[0076] Then, a thickness of the inorganic material-based article (sheet)containing the inorganic material-based dried gel fine fibers isadjusted by a press roll 6, and the inorganic material-based article(sheet) containing the inorganic material-based dried gel fine fibers isseparated from the support 4, and wound on a winding roll 10 via a guideroll 10 a.

[0077] By the above process, the inorganic material-based articleconsisting essentially of the inorganic material-based dried gel finefibers can be obtained.

[0078] Alternatively, a conjugated inorganic material-based articlecontaining a layer of the inorganic material-based dried gel fine fiberson a woven fabric, a knitted fabric, a nonwoven fabric or a net can beobtained by supplying the woven fabric, the knitted fabric, the nonwovenfabric or the net as a support 4 from an unwind roll 9 via a guide roll9 a to the track of the roller 43, 42, 41, instead of the net endlessbelt support 4 used in the above-mentioned process, and moving to thestation for extruding the sol solution. The resulting conjugatedinorganic material-based article is wound on the winding roll 10 via theguide roll 10 a in the form of the integrated article after thethickness is adjusted by the press roll 6.

[0079] Further, a three-dimensional inorganic material-based article canbe obtained by supplying a three-dimensional support (not shown) such asa bellows-like support prepared by bending a plane, a cylindricalsupport, or a bowl-like support to the station for extruding the solsolution.

[0080] It is preferable that the portion for extruding the sol solutionis separated from the other portions as a spinning room 7, because thesolvents in the stock solution are evaporated, and that the spinningroom 7 is made of materials not influenced by the solvents. Further, thespinning room 7 is preferably equipped with an exhaust vent 71 capableof evacuating the evaporated solvents.

[0081] By installing an electric oven (not shown) or the like for thesintering treatment after the heater 5, the drying step and thesintering step can be successively carried out. Alternatively, theelectric oven or the like is installed instead of the heater 5 to carryout the sintering step without the drying step.

[0082] According to the manufacturing process according to the presentinvention as mention above, the inorganic material-based gel fine fiberscan be bonded by drying or sintering, without an adhesive, or theinorganic material-based dried gel fine fibers are bonded by sintering,without an adhesive. Therefore, the inorganic material-based articlewithout the disadvantages caused by an adhesive may be prepared.

[0083] According to the manufacturing process according to the presentinvention as mention above, the inorganic material-based articlecontaining the inorganic material-based dried gel ultra-fine fibershaving a fiber diameter of 2 μm or less or the inorganic material-basedsintered ultra-fine fibers having a fiber diameter of 2 μm or less canbe produced by adjusting a strength of the electric field, an amount ofthe sol solution extruded from the nozzle, an amount of the solvents inthe sol solution, or an atmosphere at the extrusion portion, moreparticularly, by changing the atmosphere with or without a gas of thesolvents same as or similar to those of the sol solution. The resultinginorganic material-based article has excellent properties, such as afiltering performance, a pliability, or a separating performance. Thepresent inorganic material-based article containing the inorganicmaterial-based dried gel ultra-fine fibers having a fiber diameter of 2μm or less or the inorganic material-based sintered ultra-fine fibershaving a fiber diameter of 2 μm or less has an excellent pliability, andcan be bent and/or incurvated into various shaped articles. For example,the inorganic material-based article can be wound on a hollow or solidcylinder, or bent to the bellows-like shape.

[0084] According to the manufacturing process according to the presentinvention as mention above, the inorganic material-based articlecontaining the inorganic material-based dried gel fine fibers having along fiber length in comparison with a fiber diameter or the inorganicmaterial-based sintered fine fibers having a long fiber length incomparison with a fiber diameter, that is, the inorganic material-basedarticle containing the inorganic material-based dried gel fine longfibers having a high aspect ratio (fiber length/fiber diameter) or theinorganic material-based sintered fine long fibers having a high aspectratio can be produced. The inorganic material-based dried gel fine longfibers or the inorganic material-based sintered gel fine long fibers arehardly dropped from the inorganic material-based article.

[0085] According to the manufacturing process according to the presentinvention as mention above, the inorganic material-based articlecontaining the inorganic material-based dried gel fine fibers or theinorganic material-based sintered fine fibers having a fiber diameter CVvalue (standard deviation/average fiber diameter) of 0.8 or less can beproduced. The term “fiber diameter” as used herein with respect to afiber having a circular cross-sectional shape means a diameter of thecircle. For a fiber having a non-circular cross-sectional shape, adiameter of a circle having an area the same as that of the non-circularcross-sectional shape is regarded as a diameter. The term “average fiberdiameter” as used herein means an average of fiber diameters of 100fiber points, and the term “standard deviation” as used herein means avalue obtained from fiber diameters of 100 fiber points. The inorganicmaterial-based article containing inorganic material-based dried gelfine fibers or the inorganic material-based sintered fine fibers havinga CV value of 0.8 or less is preferable, because it has an uniformperformance. The CV value is preferably 0.7 or less, more preferably 0.6or less, particularly preferable 0.5 or less, most preferably 0.4 orless.

[0086] The inorganic material-based article produced by the processaccording to the present invention may be preferably used, for example,as a filtration material for an HEPA filter, a filtration material for aULPA filter, a filtration material for a clean room filter, a filtrationmaterial for a pure water filter, a filtration material for a heatresistant filter, a filtration material for an exhaust gas filter, afiltration material for a liquid filter, a substrate for carrying anoptical catalyst, a battery separator, a substrate for a printsubstrate, a catalyst sheet, an electromechanical transducer element, asheet for releasing fine bubbles, a catalyst combustion sheet, acovering material for a solar battery, a space material for liquidcrystal, a heat insulating material, or the like.

[0087] The present invention also relates to the inorganicmaterial-based article containing the inorganic material-basedultra-fine long fibers having an average fiber diameter of 2 μm or less,and composed mainly of an inorganic component. The inorganicmaterial-based article containing the inorganic material-basedultra-fine long fibers according to the present invention can beprepared by, for example, the above mentioned manufacturing processaccording to the present invention.

[0088] The inorganic material-based article containing the inorganicmaterial-based ultra-fine long fibers having an average fiber diameterof 2 μm or less has an excellent pliability, and can exhibit variousexcellent functions such as a filtering performance or sufficientlyexhibit functions of functional substances because of a large surfacearea. The average fiber diameter is preferably 1 μm or less, morepreferably 0.5 μm or less. The lower limit of the average fiber diameteris not particularly limited, but is preferably about 0.01 μm.

[0089] The average fiber diameter of the inorganic material-basedultra-fine long fiber is 2 μm or less, and therefore, the inorganicmaterial-based ultra-fine long fiber may contain a portion having afiber diameter of more than 2 μm. However, it is preferable that anyportions in the inorganic material-based ultra-fine long fiber have afiber diamter of 2 μm or less, more preferably 1 μm or less, mostpreferably 0.5 μm or less.

[0090] The inorganic material-based article containing the inorganicmaterial-based ultra-fine long fibers hardly releases the fibers,because the constituent fiber is long.

[0091] The inorganic material-based ultra-fine long fibers contained inthe inorganic material-based article according to the present inventionare composed mainly of inorganic components. That is, the inorganiccomponents account for 50 mass % or more, preferably 60 mass % or more,more preferably 75 mass % or more.

[0092] The elements of the inorganic components are not particularlylimited, but for example, are the elements enumerated with reference tothe sol solution forming step (1) of the manufacturing process of thepresent invention, and the compound, such as oxide, containing theelements are for example those enumerated with reference to the solsolution forming step (1) of the manufacturing process of the presentinvention.

[0093] The inorganic material-based ultra-fine long fibers in theinorganic material-based article of the present invention may containorganic components in addition to the inorganic components. The organiccomponents may be those enumerated with reference to the sol solutionforming step (1) of the manufacturing process of the present invention,for example, a silane coupling agent, an organic low-molecular compoundsuch as a dyestuff, an organic high-molecular compound such aspolymethyl methacrylate.

[0094] The inorganic material-based ultra-fine long fibers may containinorganic or organic fine particles therein as mentioned with referenceto the manufacturing process of the present invention. The fineparticles can reside in the fibers according to a method as mentionedwith reference to the manufacturing process of the present invention.

[0095] The present inorganic material-based article containing theinorganic material-based ultra-fine long fibers hardly releases fibersand has an excellent pliability, because it contains the inorganicmaterial-based ultra-fine long fibers. An amount of the inorganicmaterial-based ultra-fine long fibers in the present inorganicmaterial-based article is not particularly limited, but is preferably 1mass % or more, more preferably 5 mass % or more with respect to thewhole mass of the inorganic material-based article excluding the mass ofthe support. In this connection, it is noted that the present inorganicmaterial-based article may contain the powder material or the fineparticles.

[0096] When the inorganic material-based ultra-fine long fibers in thepresent inorganic material-based article are bonded to each other atcontacting surfaces without an adhesive, the inorganic material-basedarticle according to the present invention does not substantiallycontain an adhesive, or thus suppresses the release of pollutants.

[0097] The inorganic material-based ultra-fine long fibers forming thepresent inorganic material-based article may be, for example, in theform of a dried gel, an incompletely sintered gel, or completelysintered gel.

[0098] The present inorganic material-based article may be a mixture orconjugation of the inorganic material-based ultra-fine long fibers withorganic material-based fibers, inorganic material-based thick fibershaving a fiber diameter of more than 2 μm, inorganic material-basedshort fibers, or yarns thereof, a woven fabric thereof, a knitted fabricthereof, a nonwoven fabric thereof, a net thereof, the powder material,or the like. various properties such as a strength or an easiness ofshaping may be enhanced in the present inorganic material-based article,and applied to various field, by such a mixture or conjugation.

[0099] The present inorganic material-based article has an excellentpliability, and can be of any shape, such as a sheet, a plate, a block,a hollow or solid cylinder, or the like.

[0100] The present inorganic material-based article containing theinorganic material-based ultra-fine long fibers can be prepared by, forexample, the process according to the present invention. However, anamount of the sol solution extruded from the nozzle, the viscosity ofthe sol solution, the solvents of the sol solution, a strength of theelectric field, or a selection of the compounds containing theabove-mentioned elements should be appropriately adjusted so as toobtain long fibers having an average fiber diameter of 2 μm or less,when spun. The above conditions may be easily determined by repeatingexperiments.

[0101] In the drying step (3) of the manufacturing process of thepresent invention, the inorganic material-based gel fine long fibers aredried under the integrated condition with the support to obtain theinorganic material-based article containing the inorganic material-baseddried gel ultra-fine long fibers integrated with the support; or theinorganic material-based gel fine long fibers are dried on the support,and the inorganic material-based dried gel ultra-fine long fibers areseparated from the support to obtain the inorganic material-basedarticle consisting essentially of the inorganic material-based dried gelultra-fine long fibers. In both cases, the constituent fibers are bondedto each other without an adhesive, and the fibers are hardly droppedfrom the article.

[0102] In the manufacturing process according to the present invention,the sintering step (4) may be carried out after the collecting step (2),without carrying out the drying step (3). For example, when theinorganic material-based article containing inorganic components andorganic components is sintered in a range from about 200° C. or more toa temperature below a decomposition temperature of the organiccomponents, the inorganic material-based article containing remainedorganic components can be obtained, and thus, the resulting inorganicmaterial-based article can exhibit functions of the remained organiccomponents. In the inorganic material-based article obtained bysintering as above, the fibers are bonded by sintering to each other,and hardly dropped from the article. Further, when the inorganicmaterial-based article containing inorganic components and organiccomponents is sintered over a decomposition temperature of the organiccomponents, the inorganic material-based article consisting essentiallyof the inorganic components and having excellent strength and heatresistance can be obtained.

[0103] In the manufacturing process according to the present invention,the inorganic material-based article containing the inorganicmaterial-based sintered ultra-fine long fibers having the remainedorganic components, or the inorganic material-based article containingthe inorganic material-based sintered ultra-fine long fibers consistingessentially of the inorganic components and having an excellent strengthand heat resistance can be obtained, by successively carrying out thedrying step (3) and the sintering step (4) after the collecting step(2).

[0104] The present inorganic material-based article containing theinorganic material-based ultra-fine long fibers having a CV value of 0.8or less is preferable, because it has an uniform performance. The CVvalue is preferably 0.7 or less, more preferably 0.6 or less,particularly preferable 0.5 or less, most preferably 0.4 or less.

[0105] The present inorganic material-based article containing theinorganic material-based ultra-fine long fibers hardly releases fiberstherefrom, has excellent pliability, a wide surface area, and anexcellent heat resistance, and hardly release pollutants. Therefore, itmay be preferably used, for example, as a filtration material for anHEPA filter, a filtration material for a ULPA filter, a filtrationmaterial for a clean room filter, a filtration material for a pure waterfilter, a filtration material for a heat resistant filter, a filtrationmaterial for an exhaust gas filter, a filtration material for a liquidfilter, a substrate for carrying an optical catalyst, a batteryseparator, a substrate for a print substrate, a catalyst sheet, anelectromechanical transducer element, a sheet for releasing finebubbles, a catalyst combustion sheet, a covering material for a solarbattery, a space material for liquid crystal, a heat insulatingmaterial, or the like.

[0106] The present invention also relates to a substrate for a circuitboard, comprising a fiber sheet containing inorganic material-basedultra-fine fibers having an average fiber diameter of 2 μm or less, andcomposed mainly of an inorganic component. The substrate exhibits anexcellent reliable insulation quality and a laser workability, and itsufficiently meets the requirement for the miniaturization and highperformance of a circuit board.

[0107] The thinner the average fiber diameter of the inorganicmaterial-based ultra-fine fibers for the substrate has, the moreexcellent laser workability the circuit board of the present inventioncan exhibit. The average fiber diameter is preferably 1 μm or less, morepreferably 0.5 um or less. The lower limit of the average fiber diameterof the inorganic material-based ultra-fine fibers is not particularlylimited, so long ps a matrix resin can be uniformly impregnated, but ispreferably about 0.01 μm.

[0108] The average fiber diameter of the inorganic material-basedultra-fine fiber for the substrate is 2 μm or less, and therefore, theinorganic material-based ultra-fine fiber may contain a portion having afiber diameter of more than 2 μm. However, it is preferable that anyportions in the inorganic material-based ultra-fine fiber have a fiberdiamter of 2 μm or less, more preferably 1 μm or less, most preferably0.5 μm or less.

[0109] The inorganic material-based ultra-fine fibers for the substratecontains the inorganic components as a main component (50 mass % ormore) so that it exhibits the reliable insulation quality and maintainsa good dimensional stability even when heated. It is preferable that theinorganic material-based ultra-fine fibers for the substrate contains 50mass % or more, more preferably 75 mass % or more, most preferably 99.9mass % of silica components (SiO₂), in view of the dielectriccharacteristics of the circuit board. In particular, the inorganicmaterial-based ultra-fine fiber containing 99.9 mass % of the silicacomponents has a dielectric constant of 3.8, that is, a low value incomparison with other glass compositions. Therefore, it is suitable as asubstrate for the circuit board meeting the high-frequency requirement.

[0110] The inorganic component other than the silica component is notparticularly limited, but for example, Al₂O₃, B₂O₃, CaO, MgO, K₂O, Na₂O,TiO₂, ZrO₂, CeO₂, SnO₂, Fe₂O₃, V₂O₅, CdO, WO₃, Nb₂O₅, Ta₂O₅, In₂O₃,GeO₂, PbO, PbTi₄O₉, LiNbO₃, BaTiO₃, PbZrO₃, KTaO₃, Li₂B₄O₇, NiFe₂O₄,SrTiO₃. The inorganic component may be composed of one or more oxides asabove. The inorganic material-based ultra-fine fibers for the substratemay have a composition from an E glass composition to Q glass (silicaglass) composition by combining the above inorganic components, and maybe applied to substrates having various grades.

[0111] The inorganic material-based ultra-fine fibers for the substratemay contain organic components in addition to the above-memtionedinorganic components. The organic components may be, for example, asilane coupling agent, titanium coupling agent or the like.

[0112] It is preferable that the inorganic material-based ultra-finefibers for the substrate are long fibers. The substrate containing theinorganic material-based ultra-fine long fibers can suppress the fuzzingor the dropping of the fibers during an impregnating step of a matrixresin, a step of processing the circuit board, such as a step ofproducing holes or cutting the circuit board.

[0113] The substrate of the present invention comprises a fiber sheet,such as a woven fabric or a nonwoven fabric, containing theabove-mentioned inorganic material-based ultra-fine fibers. Thesubstrate preferably comprises the nonwoven fabric, in view of asmoothness of the surface and an apparent density. That is, thesubstrate having a nonwoven fabric structure exhibits a smoothness moreexcellent than the substrate having a woven fabric structure, becausethe former does not contain a portion where yarns are crossed to eachother as in the latter. Further, an apparent density of the substratehaving a nonwoven fabric structure even with fine fibers does not becometoo high, and an excellent permeability of a matrix resin can beobtained.

[0114] The substrate of the present invention comprises the fiber sheetcontaining the above-mentioned inorganic material-based ultra-finefibers. However, the substrate may contain, in addition to theabove-mentioned inorganic material-based ultra-fine fibers, organicmaterial-based ultra-fine fibers (average fiber diameter=2 μm or less),inorganic material-based thick fibers (average fiber diameter=more than2 μm), organic material-based thick fibers (average fiber diameter=morethan 2 μm), or an adhesive. It is preferable that the fibers forming thesubstrate of the present invention consist essentially of the inorganicmaterial-based ultra-fine fibers, in view of a reliable insulationquality or a laser workability, Further, it is preferable that thesubstrate of the present invention consists essentially of the inorganicmaterial-based ultra-fine fibers, but does not contain an adhesive. Inthe substrate wherein the fibers are bonded without an adhesive at thecrossing portions thereof, a poor penetration of a matrix resin causedby a formation of the adhesive resin coating can be prevented during theproduction of the circuit board. Further, it can prevent impurity fromreleasing. Therefore, the circuit board having a long-term reliableinsulation quality can be produced.

[0115] The thickness of the substrate of the present invention ispreferably 80 μm or less, so that the substrate can contribute theminiaturization of the circuit board. The thinner the thickness of thesubstrate is in a range where an insulation is insured, the smaller thecircuit board becomes. The thickness of the substrate is preferably 60μm or less, more preferably 50 μm or less. The lower limit of thethickness of the substrate is not particularly limited, so long as thesubstrate has a strength capable of withstanding an impregnation processwith a matrix resin, but is suitably about 10 μm. The term “thickness”as used herein means a value determined by a method defined in JIS B7502, that is, a value measured by an outside micrometer under 5N load.

[0116] A mass per unit area and an apparent density of the substrate ofthe present invention are not particularly limited, but a mass per unitis preferably 3 to 30 g/m², because an excellent mechanical strength canbe obtained, and an apparent density is preferably 0.05 to 0.5 g/cm³.The mass per unit area means a basis weight measured by a method definedin JIS P 8124, a method for measuring a basis weight of paper and board,and the apparent density is a value obtained by dividing the basisweight by the thickness.

[0117] The substrate of the present invention may be prepared by, forexample, the following process comprising the steps of

[0118] (1) forming a sol solution mainly composed of an inorganiccomponent [the sol solution forming step as above],

[0119] (2) producing inorganic material-based gel ultra-fine long fibersby extruding the resulting sol solution from a nozzle, and at the sametime, applying an electrical field to the extruded sol solution to thinthe extruded sol solution, and then, collecting inorganic material-basedgel ultra-fine fibers on a support [the collecting step as above], andthen,

[0120] (3) drying or drying and sintering the collected inorganicmaterial-based gel ultra-fine long fibers to produce the fiber sheetcontaining inorganic material-based ultra-fine long fibers [the dryingstep as above or the sintering step as above]. According to theabove-mentioned process, the nonwoven fabric substrate consistingessentially of the inorganic material-based ultra-fine long fibershaving an average fiber diameter of 2 μm or less, and composed mainly ofan inorganic component can be prepared. That is, the nonwoven fabricsubstrate wherein the inorganic material-based ultra-fine long fibersare bonded to each other at. crossing portions without an adhesive canbe obtained, The above sol solution forming step (1), the collectingstep (2), the drying step (3), and the sintering step (4) can be carriedout as mentioned above.

[0121] When the stock solution used in the sol solution forming step (1)comprises the oxide compound containing 50 mass % or more ofsilane-based compound, the inorganic material-based ultra-fine longfibers containing 50 mass % or more of silica components can beobtained. The oxide compound may contain an organic component. Forexample, when the silane-based compound is used as the oxide compound,the silane-based compound may be modified with an organic group, such asa methyl or epoxy group.

[0122] In the collecting step (2), the inorganic material-based gelultra-fine short fibers may be produced by intermittently extruding thesol solution from the nozzle, and collected on the support. Further, thenozzles for extruding the inorganic material-based gel ultra-fine shortfibers may be placed in juxtaposition with the nozzles for extruding theinorganic material-based gel ultra-fine long fibers so that a mixture ofthe inorganic material-based gel ultra-fine short fibers and theinorganic material-based gel ultra-fine long fibers can be collected onthe support. While the inorganic material-based gel ultra-fine longfibers are drawn from the nozzle to the support, organic material-basedultra-fine fibers having an average diameter of 2 μm or less, inorganicmaterial-based thick fibers having an average diameter of more than 2μm, organic material-based thick fibers having an average diameter ofmore than 2 μm, or adhesives may be supplied thereto so that a mixturethereof can be collected on the support.

[0123] When the inorganic material-based dried or sintered ultra-finelong fibers having an average diameter of 2 μm or less should beobtained, the average diameter of the inorganic material-based gel finelong fibers before dried and/or sintered does not need to be 2 μm orless. For example, an average diameter of 3 μm or less is sufficient toobtain the inorganic material-based dried or sintered ultra-fine longfibers having an average diameter of 2 μm or less, because the inorganicmaterial-based gel fine long fibers are shrunk to some degree in thedrying step (3) and/or the sintering step (4).

[0124] The circuit board of the present invention may be prepared byapplying a matrix resin of a thermosetting resin to the substrate of thepresent invention. Therefore, the circuit board of the present inventioncan be well treated by a laser without disadvantages that a shape of theproduced hole may not be accurate, a production of holes cannot besmoothly carried out, or fiber fuzzes are released. Further, the circuitboard of the present invention has an excellent reliable insulationquality.

[0125] The thermosetting resin, that is, the matrix resin, which may beused for the circuit board of the present invention is not particularlylimited, but may be, for example, a phenolic resin, an epoxy resin, apolyimide resin, an isocyanate resin, an unsaturated polyester resin, ora maleimide resin. Further, a resin composition prepared by blending orreacting two or more above-mentioned resins; a modified resin preparedby modifying one or more the above-mentioned thermosetting resins withpolyvinyl butyral, acrylonitrile-butadiene rubber, a polyfunctionalacrylate compound, or an additive; a resin composition prepared from across-linking setting resin (IPN or semi-IPN) modified with across-linked polyethylene, a cross-linked polyethylene/epoxy resin, across-linked polyethylene/cyanate resin, polyphenylene/cyanate resin, orother thermosetting resin, may be also used. When the matrix resin iscomposed of at least one selected from a group of a phenolic resin, anepoxy resin, a polyimide resin, and an isocyanate resin, the circuitboard having an excellent heat resistance can be obtained.

[0126] A prepreg may be prepared by applying the above-mentionedthermosetting resin, i.e., the matrix resin, to the substrate of thepresent invention. The thermosetting resin, i.e., the matrix resin, canbe applied to the substrate by an impregnating method, a coating method,or a melt-transferring method. More particularly, there may be mentioned(1) a method wherein the substrate is impregnated with a vanish preparedby dissolving the thermosetting resin (the matrix resin) in a solvent,and then, dried, (2) a method wherein the substrate is impregnated witha liquid thermosetting resin (the matrix resin) prepared at a normaltemperature or an elevated temperature without a solvent, (3) a methodwherein powdery thermosetting resin (the matrix resin) is fixed on thesubstrate, (4) a method wherein a layer of a thermosetting resin (thematrix resin) is formed on a film or sheet having a release property,and then, the melted layer is transferred to the substrate, or the like.

[0127] The substrate carrying the thermosetting resin (the matrix resin)can be dried by, for example, an upright dryers located separatelytherefrom, to produce a prepreg.

[0128] An amount of the thermosetting resin (the matrix resin) appliedto the prepreg is not particularly limited, but is preferably 30 to 95%by weight with respect to the whole weight of the prepreg. If the amountof the thermosetting resin (the matrix resin) is less than 30% byweight, defective moldings are liable to be produced. If the amount ismore than 95% by weight, a molding becomes difficult.

[0129] The circuit board of the present invention may be prepared, usingat least one prepreg. More specifically, the circuit board of thepresent invention may be a circuit board consisting of one or moreprepregs as above, a circuit board prepared by combining one or moreprepregs as above and one or more conventional substrates such as aglass woven fabric or a glass nonwoven fabric, a circuit board carryinga metallic foil on one or both sides of the above-mentioned circuitboard, an inner layer circuit board having a printed wiring networkformed on the above-mentioned circuit board for an inner layer, amulti-layered circuit board prepared from the above-mentioned circuitboards, or the like.

[0130] The metallic foil which may be used in the circuit board carryingone or two metallic foils may be a conventional foil, such as a copperfoil, an iron foil, an aluminum foil, or an aluminum/copper foil. One orboth sides of the foil surface may be treated. A foil having an adhesivemay be used.

EXAMPLES

[0131] The present invention will now be further illustrated by, but isby no means limited to, the following Examples.

Example 1

[0132] (1) Sol Solution Forming Step

[0133] Tetraethoxysilane as a metallic compound, ethanol as a solvent,water for hydrolysis, and 1N HCl as a catalyst were mixed at a molarratio of 1:5:2:0.03, and heated under reflux at 78° C. for 10 hours.Then, the solvent was removed by a rotary evaporator. The whole washeated at 50° C. to obtain a sol solution having a viscosity of about 20poise.

[0134] (2) Collecting Step

[0135] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.5 mm at a rate of 1.2 mL/h per a nozzle.The sol solution was extruded from the nozzles. At the same time, avoltage of 25 kV was applied to the nozzles, and a stainless steelpore-free roll as a support was grounded so that an electrical field(2.5 kV/cm) was applied to the extruded sol solution to thereby thin thediameter of the extruded sol solution, produce inorganic material-basedgel fine long fibers, and collect the resulting inorganic material-basedgel fine long fibers on the rotating stainless steel pore-free roll. Adistance between the nozzles and the stainless steel pore-free roll was10 cm.

[0136] (3) Drying Step

[0137] The collected inorganic material-based gel fine long fibers weredried by a heater at 150° C. to form an inorganic material-based articlecomposed of the dried inorganic material-based gel fine long fibers madeof SiO₂ and having an average diameter of 3 μm wherein diameters of anyportions of the fibers were about 3 μm. Contacting surfaces of the driedinorganic material-based gel fine long fibers made of SiO₂ and formingthe inorganic material-based article were bonded to each other not viaan adhesive, and thus, the article will release no pollutants. Further,when the resulting inorganic material-based article was bent, no crackwas formed or no fibers were dropped.

[0138] (4) Sintering Step

[0139] The resulting dried inorganic material-based gel fine long fiberswere completely vitrified by sintering at 150° C. for 5 hours, at 300°C. for 5 hours, and then at 1000° C. to obtain an inorganicmaterial-based article composed of sintered silica glass ultra-fine longfibers having an average diameter of 2 μm wherein diameters of anyportions of the fibers were about 2 μm. Contacting surfaces of thesintered silica glass ultra-fine long fibers forming the inorganicmaterial-based article were bonded to each other not via an adhesive,and thus, the article will release no pollutants. Further, when theresulting inorganic material-based article was bent, no crack was formedor no fibers were dropped.

Example 2

[0140] The procedures described in Example 1 (1) to (3) were repeated,except that a sol solution having a viscosity of about 10 poise wasused, to obtain an inorganic material-based article composed of thedried inorganic material-based gel ultra-fine long fibers made of SiO₂,and having an average diameter of 1 μm wherein diameters of any portionsof the fibers were about 1 μm. Contacting surfaces of the driedinorganic material-based gel ultra-fine long fibers made of SiO₂ andforming the inorganic material-based article were bonded to each othernot via an adhesive, and thus, the article will release no pollutants.Further, when the resulting inorganic material-based article was bent,no crack was formed or no fibers were dropped.

[0141] Then, the inorganic material-based article composed of the driedinorganic material-based gel ultra-fine long fibers was sintered andcompletely vitrified as in Example 1 (4), to obtain an inorganicmaterial-based article composed of sintered silica glass ultra-fine longfibers having an average diameter of 0.8 μm wherein diameters of anyportions of the fibers were about 0.8 μm. Contacting surfaces of thesintered silica glass ultra-fine long fibers forming the inorganicmaterial-based article were bonded to each other not via an adhesive,and thus, the article will release no pollutants. Further, when theresulting inorganic material-based article was bent, no crack was formedor no fibers were dropped.

Example 3

[0142] The procedures described in Example 1 (1) to (3) were repeated,except that a sol solution prepared by adding butanol to adjust aviscosity to about 3.5 poise was used, a rate of the sol solution pumpedto nozzles was 0.8 mL/h per a nozzle, and the voltage applied to nozzleswas 20 kV, to obtain an inorganic material-based article composed of thedried inorganic material-based gel ultra-fine long fibers made of SiO₂,and having an average diameter of 0.6 μm wherein diameters of anyportions of the fibers were about 0.6 μm. Contacting surfaces of thedried inorganic material-based gel ultra-fine long fibers made of SiO₂and forming the inorganic material-based article were bonded to eachother not via an adhesive, and thus, the article will release nopollutants. Further, when the resulting inorganic material-based articlewas bent, no crack was formed or no fibers were dropped.

[0143] Then, the inorganic material-based article composed of the driedinorganic material-based gel ultra-fine long fibers was sintered andcompletely vitrified as in Example 1(4), to obtain an inorganicmaterial-based article composed of sintered silica glass ultra-fine longfibers having an average diameter of 0.4 μm wherein diameters of anyportions of the fibers were about 0.4 μm. Contacting surfaces of thesintered silica glass ultra-fine long fibers forming the inorganicmaterial-based article were bonded to each other not via an adhesive,and thus, the article will release no pollutants. Further, when theresulting inorganic material-based article was bent. no crack was formedor no fibers were dropped.

Example 4

[0144] The procedures described in Example 1 (1) to (3) were repeated,except that a sol solution prepared by adding butanol to adjust aviscosity to about 1.5 poise was used, a rate of the sol solution pumpedto nozzles was 0.6 mL/h per a nozzle, and the voltage applied to nozzleswas 20 kV, to obtain an inorganic material-based dried gel article,i.e., an inorganic material-based dried gel nonwoven fabric, composed ofthe inorganic material-based ultra-fine long fibers made of SiO₂ andhaving an average diameter of 0.2 μm wherein diameters of any portionsof the fibers were about 0.2 μm. Contacting surfaces of the inorganicmaterial-based ultra-fine long fibers made of SiO₂ and forming theinorganic material-based dried gel article, i.e., the inorganicmaterial-based dried gel nonwoven fabric, were bonded to each other notvia an adhesive, and thus, the article will release no pollutants.Further, when the resulting inorganic material-based dried gel nonwovenfabric was bent, no crack was formed or no fibers were dropped.

[0145] Then, the inorganic material-based dried gel article i.e., theinorganic material-based dried gel nonwoven fabric, was sintered at 150°C. for 5 hours, at 300° C. for 5 hours, and at 800° C. and completelyvitrified to obtain an inorganic material-based sintered article i.e.,an inorganic material-based sintered nonwoven fabric, composed ofinorganic material-based ultra-fine long fibers, i.e., silica glassultra-fine long fibers, having an average diameter of 0.15 μm whereindiameters of any portions of the fibers were about 0.15 μm. Contactingsurfaces of the inorganic material-based ultra-fine long fibers, i.e.,the silica glass ultra-fine long fibers were bonded to each other notvia an adhesive, and thus, the article will release no pollutants.Further, when the resulting inorganic material-based sintered nonwovenfabric was bent, no crack was formed or no fibers were dropped.

Example 5

[0146] (1) Sol Solution Forming Step

[0147] Tetraethoxysilane as a metallic compound, ethanol as a solvent,water for hydrolysis, and 1N HCl as a catalyst were mixed at a molarratio of 1:5:2:0.003, and heated under reflux at 78° C. for 15 hours.Then, the solvent was removed by a rotary evaporator. The whole washeated at 60° C. to obtain a sol solution having a viscosity of about 2poise.

[0148] (2) Collecting Step

[0149] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.7 mm at a rate of 1 mL/h per a nozzle. Thesol solution was extruded from the nozzles. At the same time, a voltageof 16.5 kV was applied to the nozzles, and a stainless steel pore-freeroll as a support was grounded so that an electrical field (1.65 kV/cm)was applied to the extruded sol solution to thereby thin the diameter ofthe extruded sol solution, produce inorganic material-based gelultra-fine long fibers, and collect the resulting inorganicmaterial-based gel ultra-fine long fibers on the rotating stainlesssteel pore-free roll. A distance between the nozzles and the stainlesssteel pore-free roll was 10 cm.

[0150] (3) Drying Step

[0151] The collected inorganic material-based gel ultra-fine long fiberswere dried by a heater at 150° C. for 1 hour to form an inorganicmaterial-based article composed of the inorganic material-based driedgel ultra-fine long fibers. Contacting surfaces of the inorganicmaterial-based dried gel ultra-fine long fibers made of SiO₂ and formingthe inorganic material-based article were bonded to each other not viaan adhesive, and thus, the article will release no pollutants.

[0152] (4) Sintering Step

[0153] The resulting inorganic material-based article composed of theinorganic material-based dried gel ultra-fine long fibers werecompletely vitrified by sintering at 800° C. for 1 hour to obtain aninorganic material-based article composed of sintered silica glassultra-fine long fibers having an average diameter of 0.6 μm whereindiameters of any portions of the fibers were about 0.6 μm. The CV valuewas 0.4. Contacting surfaces of the sintered silica glass ultra-finelong fibers forming the inorganic material-based article were bonded toeach other not via an adhesive, and thus, the article will release nopollutants. Further, when the resulting inorganic material-basedsintered article was bent, no crack was formed or no fibers weredropped.

Example 6

[0154] (1) Sol Solution Forming Step

[0155] Tetraethoxysilane as a metallic compound, ethanol as a solvent,water for hydrolysis, and 1N HCl as a catalyst were mixed at a molarratio of 1:5:2.5:0.003, and heated under reflux at 78° C. for 15 hours.Then, the solvent was removed by a rotary evaporator. The whole washeated at 60° C. to obtain a sol solution having a viscosity of about2.5 poise.

[0156] (2) Collecting Step

[0157] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.7 mm at a rate of 1 mL/h per a nozzle. Thesol solution was extruded from the nozzles. At the same time, a voltageof 17.5 kV was applied to the nozzles, and a stainless steel pore-freeroll as a support was grounded so that an electrical field (1.75 kV/cm)was applied to the extruded sol solution to thereby thin the diameter ofthe extruded sol solution, produce inorganic material-based gelultra-fine long fibers, and collect the resulting inorganicmaterial-based gel ultra-fine long fibers on the rotating stainlesssteel pore-free roll. A distance between the nozzles and the stainlesssteel pore-free roll was 10 cm.

[0158] (3) Drying Step

[0159] The collected inorganic material-based gel ultra-fine long fiberswere dried by a heater at 150° C. for 1 hour to form an inorganicmaterial-based article composed of the inorganic material-based driedgel ultra-fine long fibers. Contacting surfaces of the inorganicmaterial-based dried gel ultra-fine long fibers made of SiO₂ and formingthe inorganic material-based article were bonded to each other not viaan adhesive, and thus, the article will release no pollutants. Further,when the resulting inorganic material-based dried gel article was bent,no crack was formed or no fibers were dropped.

[0160] (4) Sintering Step

[0161] The resulting inorganic material-based article composed of theinorganic material-based dried gel ultra-fine long fibers werecompletely vitrified by Wintering at 800° C. for 1 hours to obtain aninorganic material-based article composed of sintered silica glassultra-fine long fibers having an average diameter of 0.5 μm whereindiameters of any portions of the fibers were about 0.5 μm. The Cv valuewas 0.4. Contacting surfaces of the sintered silica glass ultra-finelong fibers forming the inorganic material-based article were bonded toeach other not via an adhesive, and thus, the article will release nopollutants. Further, when the resulting inorganic material-basedsintered article was bent, no crack was formed or no fibers weredropped.

Example 7

[0162] (1) Sol Solution Forming Step

[0163] Tetraethoxysilane as a metallic compound, ethanol as a solvent,water for hydrolysis, and 1N HCl as a catalyst were mixed at a molarratio of 1:5;3:0.003, and heated under reflux at 78° C. for 15 hours.Then, the solvent was removed by a rotary evaporator. The whole washeated at 60° C. to obtain a sol solution having a viscosity of about 3poise.

[0164] (2) Collecting Step

[0165] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.7 mm at a rate of 1 mL/h per a nozzle. Thesol solution was extruded from the nozzles. At the same time, a voltageof 20 kV was applied to the nozzles, and a stainless steel pore-freeroll as a support was grounded so that an electrical field (2 kV/cm) wasapplied to the extruded sol solution to thereby thin the diameter of theextruded sol solution, produce inorganic material-based gel ultra-finelong fibers, and collect the resulting inorganic material-based gelultra-fine long fibers on the rotating stainless steel pore-free roll. Adistance between the nozzles and the stainless steel pore-free roll was10 cm.

[0166] (3) Drying Step

[0167] The collected inorganic material-based gel ultra-fine long fiberswere dried by a heater at 150° C. for 1 hour to form an inorganicmaterial-based article composed of the inorganic material-based driedgel ultra-fine long fibers. Contacting surfaces of the inorganicmaterial-based dried gel ultra-fine long fibers made of SiO₂, andforming the inorganic material-based article were bonded to each othernot via an adhesive, and thus, the article will release no pollutants.Further, when the resulting inorganic material-based dried gel articlewas bent, no crack was formed or no fibers were dropped.

[0168] (4) Sintering Step

[0169] The resulting inorganic material-based article composed of theinorganic material-based dried gel ultra-fine long fibers werecompletely vitrified by sintering at 800° C. for 1 hour to obtain aninorganic material-based article composed of sintered silica glassultra-fine long fibers having an average diameter of 0.6 μm whereindiameters of any portions of the fibers were about 0.6 μm. The CV valuewas 0.3. Contacting surfaces of the sintered silica glass ultra-finelong fibers forming the inorganic material-based article were bonded toeach other not via an adhesive, and thus, the article will release nopollutants. Further, when the resulting inorganic material-basedsintered article was bent, no crack was formed or no fibers weredropped.

Example 8

[0170] (1) Sol Solution Forming Step

[0171] Tetraethoxysilane as a metallic compound, ethanol as a solvent,water for hydrolysis, and IN HCl as a catalyst were mixed at a molarratio of 1:5:2:0.003, and heated under reflux at 78° C. for 15 hours toprepare a silica stock solution.

[0172] On the other hand, 2-propyl alcohol, aluminium sec-butoxide, andethyl acetoacetate were mixed at a molar ratio of 0.4:0.08:0.08, andheated under reflux at 78° C. for 2 hours to prepare an alumina stocksolution.

[0173] The resulting silica stock solution and the alumina stocksolution were mixed at 78° C. for 2 hours. Then, the solvent was removedby a rotary evaporator. The whole was heated at 60° C. to obtain a solsolution having a viscosity of about 2 poise.

[0174] (2) Collecting Step

[0175] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.7 mm at a rate of 1 mL/h per a nozzle. Thesol solution was extruded from the nozzles. At the same time, a voltageof 24 kV was applied to the nozzles, and a stainless steel pore-freeroll as a support was grounded so that an electrical field (2.4 kV/cm)was applied to the extruded sol solution to thereby thin the diameter ofthe extruded sol solution, produce inorganic material-based gelultra-fine long fibers, and collect the resulting inorganicmaterial-based gel ultra-fine long fibers on the rotating stainlesssteel pore-free roll. A distance between the nozzles and the stainlesssteel pore-free roll was 10 cm.

[0176] (3) Drying Step

[0177] The collected inorganic material-based gel ultra-fine long fiberswere dried by a heater at 150° C. for 1 hour to form an inorganicmaterial-based article composed of the silica-alumina inorganicmaterial-based dried gel ultra-fine long fibers. Contacting surfaces ofthe silica-alumina inorganic material-based dried gel ultra-fine longfibers forming the inorganic material-based article were bonded to eachother not via an adhesive, and thus, the article will release nopollutants.

[0178] (4) Sintering Step

[0179] The resulting inorganic material-based article composed of theinorganic material-based dried gel ultra-fine long fibers werecompletely vitrified by sintering at 1000° C. for 1 hour to obtain aninorganic material-based article composed of sintered silica-aluminaultra-fine.long fibers having an average diameter of 0.5 μm whereindiameters of any portions of the fibers were about 0.5 μm. The CV valuewas 0.22. Contacting surfaces of the sintered silica-alumina ultra-finelong fibers forming the inorganic material-based article were bonded toeach other not via an adhesive, and thus, the article will release nopollutants.

Example 9

[0180] (1) Sol Solution Forming Step

[0181] Tetraethoxysilane and methyltriethoxy silane as a metalliccompound, ethanol as a solvent, water for hydrolysis, and 1N HCl as acatalyst were mixed at a molar ratio of 0.75:0.25.5:2:0.003, and heatedunder reflux at 78° C. for 15 hours. Then, the solvent was removed by arotary evaporator. The whole was heated at 60° C. to obtain a solsolution having a viscosity of about 2 poise.

[0182] (2) Collecting Step

[0183] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.7 mm at a rate of 1 mL/h per a nozzle. Thesol solution was extruded from the nozzles. At the same time, a voltageof 17 kV was applied to the nozzles, and a stainless steel pore-freeroll as a support was grounded so that an electrical field (1.7 kV/cm)was applied to the extruded sol solution to thereby thin the diameter ofthe extruded sol solution, produce organic-inorganic (silica)-hybridmaterial-based gel ultra-fine long fibers, and collect the resultingorganic-inorganic-hybrid material-based gel ultra-fine long fibers onthe rotating stainless steel pore-free roll. A distance between thenozzles and the stainless steel pore-free roll was 10 cm.

[0184] (3) Drying Step

[0185] The collected organic-inorganic-hybrid material-based gelultra-fine long fibers were dried by a heater at 150° C. for 1 hour toform an organic-inorganic-hybrid material-based article composed of theorganic-inorganic-hybrid material-based dried gel ultra-fine longfibers. Contacting surfaces of the organic-inorganic-hybridmaterial-based dried gel ultra-fine long fibers forming theorganic-inorganic-hybrid material-based article were bonded to eachother not via an adhesive, and thus, the article will release nopollutants.

[0186] (4) Sintering Step

[0187] The resulting organic-inorganic-hybrid material-based articlecomposed of the organic-inorganic-hybrid material-based dried gelultra-fine long fibers were completely vitrified by sintering at 500° C.for 1 hour to obtain an organic-inorganic-hybrid material-based articlecomposed of sintered organic-inorganic-hybrid ultra-fine long fibershaving an average diameter of 0.5 μm wherein diameters of any portionsof the fibers were about 0.5 μm. The CV value was 0.4. Contactingsurfaces of the sintered organic-inorganic-hybrid ultra-fine long fibersforming the organic-inorganic-hybrid material-based article were bondedto each other not via an adhesive, and thus, the article will release nopollutants.

Example 10

[0188] (1) Sol Solution Forming Step

[0189] Tetraethoxysilane and methyltriethoxy silane as a metalliccompound, ethanol as a solvent, water for hydrolysis, and 1N HCl as acatalyst were mixed at a molar ratio of 0.9:0.1:5:2:0.003, and heatedunder reflux at 78° C. for 15 hours. Then, the solvent was removed by arotary evaporator. The whole was heated at 60° C. to obtain a solsolution having a viscosity of about 2 poise.

[0190] (2) Collecting Step

[0191] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.7 mm at a rate of 1 mL/h per a nozzle. Thesol solution was extruded from the nozzles. At the same time, a voltageof 17 kV was applied to the nozzles, and a stainless steel pore-freeroll as a support was grounded so that an electrical field (1.7 kV/cm)was applied to the extruded sol solution to thereby thin the diameter ofthe extruded sol solution, produce organic-inorganic (silica)-hybridmaterial-based gel ultra-fine long fibers, and collect the resultingorganic-inorganic-hybrid material-based gel ultra-fine long fibers onthe rotating stainless steel pore-free roll. A distance between thenozzles and the stainless steel pore-free roll was 10 cm.

[0192] (3) Drying Step

[0193] The collected organic-inorganic-hybrid material-based gelultra-fine long fibers were dried by a heater at 150° C. for 1 hour toform an organic-inorganic-hybrid material-based article composed of theorganic-inorganic-hybrid material-based dried gel ultra-fine longfibers. Contacting surfaces of the organic-inorganic-hybridmaterial-based dried gel ultra-fine long fibers forming theorganic-inorganic-hybrid material-based article were bonded to eachother not via an adhesive, and thus, the article will release nopollutants.

[0194] (4) Sintering Step

[0195] The resulting organic-inorganic-hybrid material-based articlecomposed of the organic-inorganic-hybrid material-based dried gelultra-fine long fibers were completely vitrified by sintering at 500° C.for 1 hour to obtain an organic-inorganic-hybrid material-based articlecomposed of sintered organic-inorganic-hybrid ultra-fine long fibershaving an average diameter of 0.8 μm wherein diameters of any portionsof the fibers were about 0.8 μm. The CV value was 0.29. Contactingsurfaces of the sintered organic-inorganic-hybrid ultra-fine long fibersforming the organic-inorganic-hybrid material-based article were bondedto each other not via an adhesive, and thus, the article will release nopollutants.

Comparative Example 1

[0196] A glass nonwoven fabric (mass per unit area=10 g/m²; thickness=90μm; apparent density=0.11 g/cm³; ratio of binder=15% by weight) wasprepared by laying E-glass chops (average fiber diameter=5 μm; fiberlength=13 mm) in accordance with a wet-laid method to obtain a websheet, spraying an acrylic binder to the resulting web sheet, and dryingand cross-linking in an oven. The CV value was 0.11. When the resultingglass nonwoven fabric was bent, many broken glass fibers were dropped,Further, when the resulting glass nonwoven fabric was heated at 400° C.for 30 minutes, a mass was reduced by 5% after heated, and a shape ofthe sheet was lost. The above results showed that the glass nonwovenfabric prepared in Comparative Example 1 released pollutants, and didnot have heat resistant.

[0197] When the inorganic material-based sintered article prepared inExample 5 was heated at 400° C. for 30 minutes, a mass was reduced by0.2% after heated, and a shape of the sheet was maintained. It isapparent that the sintered article prepared in Example 5 has anexcellent heat resistance, and releases little pollutant.

Example 11

[0198] (1) Preparation of Substrate

[0199] Tetraethoxysilane as a metallic compound, ethanol as a solvent,water for hydrolysis, and 1N HCl as a catalyst were mixed at a molarratio of 1:5;2;0.03, and heated under reflux at 78° C. for 10 hours.Then, the solvent was removed by a rotary evaporator. The whole washeated at 50° C. to obtain a sol solution having a viscosity of about 20poise.

[0200] The resulting sol solution was pumped to stainless steel nozzleshaving an inner diameter of 0.5 mm at a rate of 1.2 mL/h per a nozzle.The sol solution was extruded from the nozzles. At the same time, avoltage of 25 kV was applied to the nozzles, and a stainless steelpore-free roll as a support was grounded so that an electrical field(2.5 kV/cm) was applied to the extruded sol solution to thereby thin thediameter of the extruded sol solution, produce inorganic material-basedgel fine long fibers, and collect the resulting inorganic material-basedgel fine long fibers on the rotating stainless steel pore-free roll. Adistance between the nozzles and the stainless steel pore-free roll was10 cm.

[0201] The collected inorganic material-based gel fine long fibers werecompletely vitrified by sintering at 150° C. for 5 hours, at 300° C. for5 hours, and then at 1000° C. to obtain an inorganic material-basednonwoven fabric substrate consisting essentially of sintered silicaglass ultra-fine long fibers having an average diameter of 2 μm whereindiameters of any portions of the fibers were about 2 μm. The resultingsubstrate had a mass per unit area of 9.3 g/m², a thickness of 50 μm,and an apparent density of 0.19 g/cm³. Contacting surfaces of thesintered silica glass ultra-fine long fibers forming the inorganicmaterial-based article were bonded to each other not via an adhesive.

[0202] (2) Preparation of Prepreg

[0203] The resulting substrate was used to produce a prepreg. Moreparticularly, the substrate was impregnated with a matrix resin varnishprepared by mixing 100 parts by weight of epoxy resin (Epicoat 1001;Yuka-Shell), 4 parts by weight of dicyandiamide, and 0.5 parts by weightof benzyldimethylamine, and dried by a drier to obtain a prepregcontaining 50% by weight of the resin.

[0204] (3) Preparation of Circuit Board

[0205] A circuit board was prepared by laying two copper foils(thickness=35 μm) on both sides of the prepreg prepared in the abovestep (2), and pressing the whole at 150° C. for 50 minutes under thepressure of 300 N/cm².

Example 12

[0206] (1) Preparation of Substrate

[0207] Tetraethoxysilane as a metallic compound, ethanol as a solvent,water for hydrolysis, and 1N HCl as a catalyst were mixed at a molarratio of 1:5:2:0.03, and heated under reflux at 78° C. for 10 hours.Then, the solvent was removed by a rotary evaporator. The whole washeated at 50° C. to obtain a sol solution having a viscosity of about 10poise.

[0208] Then, the procedures described in Example 11 were repeated tocollect and completely vitrify the inorganic material-based gelultra-fine long fibers, and produce a nonwoven fabric substrateconsisting essentially of sintered silica glass ultra-fine long fibershaving an average diameter of 0.8 μm wherein diameters of any portionsof the fibers were about 0.8 μm. The resulting substrate had a mass perunit area of 9.4 g/m², a thickness of 50 μm, and an apparent density of0.19 g/cm³. Contacting surfaces of the sintered silica glass ultra-finelong fibers forming the inorganic material-based article were bonded toeach other not via an adhesive.

[0209] (2) Preparation of Prepreg

[0210] The procedures described in Example 11 were repeated except thatthe substrate prepared in Example 12 (1) was used to obtain a prepregcontaining 50% by weight of the resin.

[0211] (3) Preparation of Circuit Board

[0212] The procedures described in Example 11 were repeated except thatthe prepreg prepared in Example 12 (2) was used to obtain a circuitboard.

Example 13

[0213] (1) Preparation of Substrate

[0214] The procedures described in Example 12 were repeated, except thata sol solution prepared by adding butanol to the sol solution preparedin Example 12 to adjust a viscosity to about 3.5 poise was used, a rateof the sol solution pumped to nozzles was 0.8 mL/h per a nozzle, and thevoltage applied to nozzles was 20 kV to obtain produce a nonwoven fabricsubstrate consisting essentially of sintered silica glass ultra-finelong fibers having an average diameter of 0.4 μm wherein diameters ofany portions of the fibers were about 0.4 μm. The resulting substratehad a mass per unit area of 9.5 g/m², a thickness of 50 μm, and anapparent density of 0.19 g/cm³. Contacting surfaces of the sinteredsilica glass ultra-fine long fibers were bonded to each other not via anadhesive.

[0215] (2) Preparation of Prepreg

[0216] The procedures described in Example 11 were repeated except thatthe substrate prepared in Example 13 (1) was used to obtain a prepregcontaining 50% by weight of the resin.

[0217] (3) Preparation of Circuit Board

[0218] The procedures described in Example 11 were repeated except thatthe prepreg prepared in Example 13 (2) was used to obtain a circuitboard.

Example 14

[0219] (1) Preparation of Substrate

[0220] The procedures described in Example 12 were repeated, except thata sol solution prepared by adding butanol to the sol solution preparedin Example 12 to adjust a viscosity to about 1.5 poise was used, a rateof the sol solution pumped to nozzles was 0.6 mL/h per a nozzle, and thevoltage applied to nozzles was 20 kV to obtain produce a nonwoven fabricsubstrate consisting essentially of sintered silica glass ultra-finelong fibers having an average diameter of 0.15 μm wherein diameters ofany portions of the fibers were about 0.15 μm. The resulting substratehad a mass per unit area of 9.7 g/m², a thickness of 50 μm, and anapparent density of 0.19 g/cm³. Contacting surfaces of the sinteredsilica glass ultra-fine long fibers forming the inorganic material-basedarticle were bonded to each other not via an adhesive.

[0221] (2) Preparation of Prepreg

[0222] The procedures described in Example 11 were repeated except thatthe substrate prepared in Example 14 (1) was used to obtain a prepregcontaining 50% by weight of the resin.

[0223] (3) Preparation of Circuit Board

[0224] The procedures described in Example 11 were repeated except thatthe prepreg prepared in Example 14 (2) was used to obtain a circuitboard.

Comparative Example 2

[0225] (1) Preparation of Substrate

[0226] The procedures described in Example 11 were repeated, except thata sol solution prepared by adjusting a viscosity of the sol solutionprepared in Example 11 to about 40 poise was used, and a rate of the solsolution pumped to nozzles was 1.5 mL/h per a nozzle, to obtain anonwoven fabric substrate consisting essentially of sintered silicaglass fine long fibers having an average diameter of 3 μm whereindiameters of any portions of the fibers were about 3 μm. The resultingsubstrate had a mass per unit area of 9.7 g/m², a thickness of 50 μm,and an apparent density of 0.18 g/cm³. Contacting surfaces of thesintered silica glass fine long fibers forming the inorganicmaterial-based article were bonded to each other not via an adhesive.

[0227] (2) Preparation of Prepreg

[0228] The procedures described in Example 11 were repeated except thatthe substrate prepared in Comparative Example 2 (1) was used to obtain aprepreg containing 50% by weight of the resin.

[0229] (3) Preparation of Circuit Board

[0230] The procedures described in Example 11 were repeated except thatthe prepreg prepared in Comparative Example 2 (2) was used to obtain acircuit board.

Comparative Example 3

[0231] (1) Preparation of Substrate

[0232] A glass cloth (mass per unit area=46 g/m², thickness =60 μm;apparent density=0.77 g/m³) prepared by plain-weaving E-glass filamentshaving an average diameter of 5 μm, and then, heat-cleaning the plainweave and treating with a silane coupling agent in accordance with ausual method was used as a substrate.

[0233] (2) Preparation of Prepreg

[0234] The procedures described in Example 11 were repeated except thatthe substrate prepared in Comparative Example 3 (1) was used to obtain aprepreg containing 50% by weight of the resin.

[0235] (3) Preparation of Circuit Board

[0236] The procedures described in Example 11 were repeated except thatthe prepreg prepared in Comparative Example 3 (2) was used to obtain acircuit board.

Comparative Example 4

[0237] (1) Preparation of Substrate

[0238] A glass nonwoven fabric (mass per unit area=10 g/m²; thickness=90μm; apparent density=0.11 g/cm³; ratio of binder=15% by weight) preparedby laying E-glass chops (average fiber diameter=5 μm; fiber length=13mm) in accordance with a wet-laid method to obtain a web sheet, sprayingan acrylic binder to the resulting web sheet, and drying and crosslinking in an oven was used as a substrate.

[0239] (2) Preparation of Prepreg

[0240] The procedures described in Example 11 were repeated except thatthe substrate prepared in Comparative Example 4 (1) was used to obtain aprepreg containing 50% by weight of the resin.

[0241] (3) Preparation of Circuit Board

[0242] The procedures described in Example 11 were repeated except thatthe prepreg prepared in Comparative Example 4 (2) was used to obtain acircuit board.

[0243] Evaluation of Circuit Board

[0244] (1) Laser workability

[0245] A copper foil on the surface of each circuit board was removed byetching. Then, a laser hole of 100 μm was produced by a carbon dioxidelaser processor under the output condition of 35 mJ/pulse. After theprocessing, the resulting hole was examined by a light microscope, and ashape of the hole wall and a presence or absence of fuzzing of fiberswere evaluated.

[0246] Evaluation of the Shape of the Hole Wall:

[0247] ∘ . . . Few concave-convex structure;

[0248] Δ . . . A Few concave-convex structures;

[0249] X . . . Many concave-convex structures.

[0250] Evaluation of Fuzzing:

[0251] ∘ . . . Few fuzzing;

[0252] Δ . . . A few fuzzings;

[0253] X . . . Many fuzzings.

[0254] (2) Heat Resistance after Boiled Against Soldering

[0255] Each circuit board was boiled in water for 3 hours, and dipped ina bath of molten solder at 260° C. for 30 seconds.

[0256] ∘ . . . No abnormal portion on the circuit board;

[0257] X . . . Blisters or warpages were observed.

[0258] (3) Coefficient of Thermal Expansion

[0259] A coefficient of thermal expansion of each circuit board wasdetermined at a temperature-raising rate of 10° C./m according to a TMAmethod.

[0260] (4) Peeling Strength of Copper Foil

[0261] A peeling strength of a copper foil was determined for eachcircuit board in accordance with a method of JIS C-6481.

[0262] (5) Insulation Resistance after Pressure Cooker Treatment (PCT)

[0263] A comb-like pattern (line width=50 μm; space between lines=50 μm)was formed between terminals on each circuit board. The resultingcircuit board was treated at 121° C., under a pressure of 203 kPa, for 0hour, 100 hours, and 200 hours. Thereafter, the circuit board wasallowed to stand at 25° C., 60% RH, for 2 hours, and then a direct.current voltage of 500 V was applied for 60 seconds. Thereafter, aninsulation resistance was measured.

[0264] (6) Dielectric Characteristice

[0265] A dielectric constant and a dielectric dissipation factor weredetermined for each circuit board in accordance with a method of JISC-6481.

[0266] The results are shown in Table 1. TABLE 1 Comparative ExamplesExamples 11 12 13 14 2 3 4 Laser workability Shape of hole ◯ ◯ ◯ ◯ Δ X Δwall Fuzzing Δ ◯ ◯ ◯ Δ X X Heat resistance ◯ ◯ ◯ ◯ ◯ ◯ ◯ after boiledCoefficient of 10 8 8 7 12 18 23 thermal-expansion (ppm/° C.) Peelstrength of 14 15 15 15 12 10 13 copper foil (N/cm²) Insulationresistance after PCT (Ω) Ordinary state 6 × 10¹⁴ 7 × 10¹⁴ 6 × 10¹⁴ 8 ×10¹⁴ 6 × 10¹⁴ 7 × 10¹⁴ 5 × 10¹⁴ After 100 hours 3 × 10¹² 6 × 10¹² 2 ×10¹³ 3 × 10¹³ 2 × 10¹² 1 × 10¹² 7 × 10¹⁰ After 200 hours 2 × 10¹¹ 8 ×10¹² 6 × 10¹² 8 × 10¹² 8 × 10¹⁰ 4 × 10¹¹ <10⁸ Dielectric Characteristics(1 MHz) Dielectric 3.9 3.9 3.8 3.8 4.0 5.4 5.3 constant Dielectric 10⁻⁴10⁻⁴ 10⁻⁴ 10⁻⁴ 10⁻⁴ 10⁻³ 10⁻³ dissipation factor

[0267] As apparent from the results of the laser workability in Table 1,shapes of the hole walls were good, and few fuzzing were observed in thecircuit board of the present invention, because it is composed of theinorganic material-based ultra-fine fibers having an average fiberdiameter of 2 μm or less. Because the substrate and the matrix resin areintimately bonded to each other in the circuit board of the presentinvention, a coefficient of thermal expansion was low, and an insulationresistance after PCT was good. Further, when the circuit board of thepresent invention was composed of silica glass ultra-fine fibers, it hada low dielectric constant and a low dielectric dissipation factor, andthus would be suitable for a circuit board in a high-frequencyapplication.

[0268] On the contrary, the circuit boards prepared from the substratescomposed of inorganic material-based fibers having an average fiberdiameter of 3 to 5 μm (Comparative Examples 2 to 4) had poor laserworkability, and therefore, many and remarkable concave-convexstructures were observed on the hole walls, and many fuzzings weregenerated. Further, in the circuit board prepared from a glass nonwovenfabric substrate wherein the fibers were bonded with an adhesive at thecrossing portions thereof (Comparative Example 4), impurity from theadhesive was eluted after the PCT treatment, and thus, particularly, theinsulation resistance was lowered. The circuit board prepared from thesubstrate composed of E glass fibers (Comparative Examples 3 and 4)showed a high dielectric constant and a high dielectric dissipationfactor, and therefore was not suitable for a circuit board in ahigh-frequency application.

[0269] According to the manufacturing process of the present invention,the inorganic material-based article can be prepared by the dryingand/or sintering without an adhesive, and therefore, the disadvantagescaused by the adhesive can be avoided.

[0270] The inorganic material-based article according to the presentinvention releases little fibers, has an excellent pliability, may havevarious shapes, can be applied to various fields, and hardly releasespollutants.

[0271] The present substrate for a circuit board is formed from theinorganic material-based ultra-fine fibers having an average fiberdiameter of 2 μm or less, and composed mainly of an inorganic component,and therefore has an excellent laser workability, and an excellentreliable insulation quality.

[0272] The present substrate for a circuit board may contain theinorganic material-based ultra-fine fibers composed of 50 mass % or moreof a silica component, and thus, may be applied to various applications.In particular, the substrate composed of the silica glass ultra-finefibers has a low dielectric constant and a low dielectric dissipationfactor, and can contribute to an high-frequency application.

[0273] The present substrate consisting essentially of the nonwovenfabric structure has an excellently smooth surface, a low apparentdensity, an excellent permeability of the matrix resin althoughcontaining the inorganic material-based ultra-fine fibers. Therefore, aprepreg or a circuit board can be stably produced.

[0274] The present substrate consisting essentially of the inorganicmaterial-based ultra-fine fibers has an excellent permeability of thematrix resin into the inside of the substrate for a circuit board, andimpurities were not eluted therefrom. Therefore, a circuit board havingan excellent insulating property can be produced.

[0275] The present substrate containing the inorganic material-basedultra-fine long fibers releases little fuzzing during the step ofproducing a circuit board. Therefore, a prepreg or a circuit board canbe stably produced.

[0276] The present substrate having a thickness of as thin as 80 μm orless can contribute to the miniaturization of an electronic components.

[0277] The circuit board of the present invention prepared from thesubstrate as above has an excellent laser workability and reliableinsulation quality.

[0278] As above, the present invention was explained with reference toparticular embodiments, but modifications and improvements obvious tothose skilled in the art are included in the scope of the presentinvention.

1-6. (canceled).
 7. An inorganic material-based article comprisinginorganic material-based ultra-fine long fibers having an average fiberdiameter of 2 μm or less, and composed mainly of an inorganic component.8. The inorganic material-based article according to claim 7, whereincontacting surfaces of the inorganic material-based ultra-fine longfibers are bonded to each other not via an adhesive.
 9. The inorganicmaterial-based article according to claim 7, wherein a CV value of theinorganic material-based ultra-fine long fiber in the inorganicmaterial-based article is 0.8 or less.
 10. A substrate for a circuitboard, comprising a fiber sheet containing inorganic material-basedultra-fine fibers having an average fiber diameter of 2 μm or less, andcomposed mainly of an inorganic component.
 11. The substrate for acircuit board according to claim 10, wherein a silica componentcontained in the inorganic material-based ultra-fine fiber is 50 mass %or more.
 12. The substrate for a circuit board according to claim 10,wherein the fiber sheet is a nonwoven fabric.
 13. The substrate for acircuit board according to claim 10, wherein the fiber sheet consistsessentially of the inorganic material-based ultra-fine fibers.
 14. Thesubstrate for a circuit board according to claim 10, wherein theinorganic material-based ultra-fine fibers consist essentially of longfibers.
 15. The substrate for a circuit board according to claim 10,wherein a thickness of the substrate is 80 μm or less.
 16. A circuitboard containing the substrate according to claim 10.